Glioblastoma is the most aggressive type of solid cancer that begins within the brain. We previously demonstrated that photodynamic therapy using talaporfin sodium (TS-PDT) treatment exhibits anti-tumor activity against glioblastoma. In this study, we found that sodium arsenite selectively decreased the cell viability of U251 glioblastoma cell line. Moreover, arsenite enhanced the anti-tumor activity of TS-PDT in the cells. These results suggest that arsenite has the potential to exhibit anti-tumor activity against U251 glioblastoma cell line and enhance the anti-tumor effect of TS-PDT.